This invention relates to electronic filters of the bandpass type, and more particularly to bandpass filters in which the center frequency and the bandpass are controllable.
Electronic signal filters are ubiquitous in modern equipments, taking on innumerable low pass, bandpass and high pass configurations. The physical implementations change with advances in technology. Filters at 455 KHz for AM radios were at one time considered to be at a relatively high frequency, and were implemented using then advanced techniques. At the current state of the art, such filters are well within the "low" frequency range, and may be implemented in a variety of now-conventional manners.
For some purposes, as for example for spectrum analysis, or for system reconfiguration in communication satellites, it may be desirable to have filters in which the cutoff frequency of frequencies are adjustable, and also in which the bandwidth or bandpass is adjustable. At one time, such adjustments could be made only by mechanical tuning, using screw-mounted slugs and the like. Control speed, reliability and simplicity are enhanced by filters which are adjustable in frequency and passband by electronic signals.